He's saying your 95% of matches are 1 sided because some players go into the game with a losing attitude, get defensive over legimate advice, and generally decide to make poor choices/not play the game, which gives the other team an easy win.
And he's not wrong. That's mostly what happens. The other is that most low elo game players rely on "luck" rather than "skill" and generally pull near 50% wins by Yoloing, so they never learn from mistakes. They just blame their 50% on other players, and don' realize that often, their yolo set up the loss.
You have no idea how many players when you call them out on feeding 0/5 after they get toxic, they simply blame the team for not covering them. They made no faults farming way out in lane and getting jungle ganked 5 times in a row. They made no faults not religiously warding in a game where they placed 4 wards total. They made no mistakes chasing low HP targets into an unwarded enemy jungle. They just don't understand, that what they did, laid a 2-3k gold advantage laner on the rest of their team, which is enough to allow their kits to have the value of 2 champs in sustainable damage at a fast pace.